spi: dt-bindings: amlogic, meson-gx-spicc: add Amlogic G12A compatible

The Amlogic G12A SPICC controllers uses a secondary clock used to feed the
baud rate generator and the delay control logic.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20200312133131.26430-9-narmstrong@baylibre.com


Signed-off-by: Mark Brown <broonie@kernel.org>